A detailed study on thiocarbonyl ene reactions

Thiocarbonyl ene reactions via CS and CC bond formation routes have been performed using DFT method at B3LYP/6-31G**//B3LYP/6-31G* level, indicating that both routes undergo concerted mechanism. The reactions with 10 substituents on enophile were further examined. It was found that substituent affects the activation energy and regioselectivity. An electron withdrawing group lowers the activation energy and prefers the CS bond formation pathway, while the reaction with an electron donating group prefers the CC bond formation route with higher barrier. It is worth noting that a very strong electron donating group is kinetically and thermodynamically unfavorable for the thiocarbonyl ene reaction. The substitution effect was explained by the reactivity index and charge transfer. And the charge difference on C1 and S in enophile controls the regioselectivity.